As you say you get the beep, I wouldn't be looking at the pdc unit first,

If you put the car in reverse, with the ignition to 2 listen at the sensors for a clicking,

If none of them click you may have a problem with the wireing from the pdc unit,

well thanks again for the diagnostic check as the 2 sensors on the drivers side weren't clicking while the other 2 were

I would spray them with WD40 but you didn't mention how easy it is to push them in as I gave them a little prod and they disappeared into the bumper . Looks like I've got to take the bumper off when I get time

is it OK if I swap the sensors when the bumper is off to see if it's the sensors or the wiring as I presume they are all the same part?

i sense somebody else may have had a play with them, they use two clips either side of them to hold them in and they are rather hard to get out

either it wernt in properly or the clips are broken,

yup you can swap the two sensor's that dont work for the two sensors that do work,

they are all exactly the same, and they are not possition dependent

now you say that it's obvious someone has had a fiddle with it before as they simply slid straight in with no resistance. I've got some new sensors thanks to my mate but don't have them to hand as they are in my other car in his garage.

do you know if the clip is part of the sensor and mine may be broken or are the separate parts? If they are separate then I presume they will be cheap so I will buy the clips so I at least have them when the bumper is off rather than finding out I need them when I do take it off. If they are part of the sensor then I've got new sensors

I've just done a search and got 2 thread results, one being your guide. I noticed your guide shows a pic and it seems to have one way clips. Anyway, after reading through the guide it shouldn't take as long as I thought sp I'll drop my bumper Saturday